Nutrient Response to Land Management Alterations in the Miombo Woodlands Region

Walker, Sarah Margaret, Department of Environmental Sciences, University of Virginia
Shugart, Hank, Department of Environmental Sciences, University of Virginia
Lawrence, Deborah, Department of Environmental Sciences, University of Virginia
Macko, Stephen, Department of Environmental Sciences, University of Virginia
Swap, Robert, Department of Environmental Sciences, University of Virginia

South-central Africa is undergoing increased agricultural intensification, however, the long term ecological response is unknown. Through fieldwork and modeling, the short to long term impact on nutrient stocks of crop-fallow agriculture and selective logging are examined in the Miombo Woodlands of south-central Africa. Based on field measurements, initial crop production does not result in significant soil carbon, nitrogen, or phosphorus reductions in rural Tanzania and Mozambique. In rural Tanzania only surface level carbon stocks were reduced in areas with short cultivation periods followed by equal or longer fallow periods. In Malawi, areas under crop production for many years had significantly lower soil nutrient levels than Miombo Woodland areas. The CENTURY model was parameterized and accurately modeled the Miombo system. When agricultural intensity is increased, modeled system nutrient levels decline over the short and long term. Commonly practiced fallow lengths are not long enough to allow complete soil nutrient recovery. Based on modeled results, selective logging for charcoal production with a rotation cycle greater than ten years is sustainable in the long term. It is recommended that only larger wood and branches be removed from woodland areas and smaller branches and leaves left in place to decompose. There is an escalating demand for climate change mitigation measures, creating an international market for greenhouse gas emission reductions. Communities in the Miombo region can participate in this market by working together to alter the land management in a way that results in quantifiable carbon emission reductions or carbon ii sequestration. The carbon and economic impact of increasing fallow periods and logging rotations was examined. Assuming the current average carbon price, at the community scale it will be economically advantageous to elevate the fallow period from five to fifteen years and sell resulting carbon credits. A minimum price of US$28 t CO 2 e -1 would be needed before it would become more profitable to increase logging rotations to 30 years. These preliminary results suggest potential for the region to participate in the carbon market. It is recommended that this type of analysis be expanded to include a greater number of activity types and encompass a larger area.

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PHD (Doctor of Philosophy)
agriculture, South-central Africa
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